/*

 * jdhuff.c

 *

 * Copyright (C) 1991-1995, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 * This file contains Huffman entropy decoding routines.

 *

 * Much of the complexity here has to do with supporting input suspension.

 * If the data source module demands suspension, we want to be able to back

 * up to the start of the current MCU.  To do this, we copy state variables

 * into local working storage, and update them back to the permanent

 * storage only upon successful completion of an MCU.

 */



#define JPEG_INTERNALS

#include "jinclude.h"

#include "jpeglib.h"

#include "jdhuff.h"		/* Declarations shared with jdphuff.c */





/*

 * Expanded entropy decoder object for Huffman decoding.

 *

 * The savable_state subrecord contains fields that change within an MCU,

 * but must not be updated permanently until we complete the MCU.

 */



typedef struct {

  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */

} savable_state;



/* This macro is to work around compilers with missing or broken

 * structure assignment.  You'll need to fix this code if you have

 * such a compiler and you change MAX_COMPS_IN_SCAN.

 */



#ifndef NO_STRUCT_ASSIGN

#define ASSIGN_STATE(dest,src)  ((dest) = (src))

#else

#if MAX_COMPS_IN_SCAN == 4

#define ASSIGN_STATE(dest,src)  \

	((dest).last_dc_val[0] = (src).last_dc_val[0], \

	 (dest).last_dc_val[1] = (src).last_dc_val[1], \

	 (dest).last_dc_val[2] = (src).last_dc_val[2], \

	 (dest).last_dc_val[3] = (src).last_dc_val[3])

#endif

#endif





typedef struct {

  struct jpeg_entropy_decoder pub; /* public fields */



  /* These fields are loaded into local variables at start of each MCU.

   * In case of suspension, we exit WITHOUT updating them.

   */

  bitread_perm_state bitstate;	/* Bit buffer at start of MCU */

  savable_state saved;		/* Other state at start of MCU */



  /* These fields are NOT loaded into local working state. */

  unsigned int restarts_to_go;	/* MCUs left in this restart interval */



  /* Pointers to derived tables (these workspaces have image lifespan) */

  d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];

  d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];

} huff_entropy_decoder;



typedef huff_entropy_decoder * huff_entropy_ptr;





/*

 * Initialize for a Huffman-compressed scan.

 */



METHODDEF void

start_pass_huff_decoder (j_decompress_ptr cinfo)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  int ci, dctbl, actbl;

  jpeg_component_info * compptr;



  /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.

   * This ought to be an error condition, but we make it a warning because

   * there are some baseline files out there with all zeroes in these bytes.

   */

  if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||

      cinfo->Ah != 0 || cinfo->Al != 0)

    WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);



  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

    compptr = cinfo->cur_comp_info[ci];

    dctbl = compptr->dc_tbl_no;

    actbl = compptr->ac_tbl_no;

    /* Make sure requested tables are present */

    if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||

	cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)

      ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);

    if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||

	cinfo->ac_huff_tbl_ptrs[actbl] == NULL)

      ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);

    /* Compute derived values for Huffman tables */

    /* We may do this more than once for a table, but it's not expensive */

    jpeg_make_d_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],

			    & entropy->dc_derived_tbls[dctbl]);

    jpeg_make_d_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],

			    & entropy->ac_derived_tbls[actbl]);

    /* Initialize DC predictions to 0 */

    entropy->saved.last_dc_val[ci] = 0;

  }



  /* Initialize bitread state variables */

  entropy->bitstate.bits_left = 0;

  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */

  entropy->bitstate.printed_eod = FALSE;



  /* Initialize restart counter */

  entropy->restarts_to_go = cinfo->restart_interval;

}





/*

 * Compute the derived values for a Huffman table.

 * Note this is also used by jdphuff.c.

 */



GLOBAL void

jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl,

			 d_derived_tbl ** pdtbl)

{

  d_derived_tbl *dtbl;

  int p, i, l, si;

  int lookbits, ctr;

  char huffsize[257];

  unsigned int huffcode[257];

  unsigned int code;



  /* Allocate a workspace if we haven't already done so. */

  if (*pdtbl == NULL)

    *pdtbl = (d_derived_tbl *)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  SIZEOF(d_derived_tbl));

  dtbl = *pdtbl;

  dtbl->pub = htbl;		/* fill in back link */

  

  /* Figure C.1: make table of Huffman code length for each symbol */

  /* Note that this is in code-length order. */



  p = 0;

  for (l = 1; l <= 16; l++) {

    for (i = 1; i <= (int) htbl->bits[l]; i++)

      huffsize[p++] = (char) l;

  }

  huffsize[p] = 0;

  

  /* Figure C.2: generate the codes themselves */

  /* Note that this is in code-length order. */

  

  code = 0;

  si = huffsize[0];

  p = 0;

  while (huffsize[p]) {

    while (((int) huffsize[p]) == si) {

      huffcode[p++] = code;

      code++;

    }

    code <<= 1;

    si++;

  }



  /* Figure F.15: generate decoding tables for bit-sequential decoding */



  p = 0;

  for (l = 1; l <= 16; l++) {

    if (htbl->bits[l]) {

      dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */

      dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */

      p += htbl->bits[l];

      dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */

    } else {

      dtbl->maxcode[l] = -1;	/* -1 if no codes of this length */

    }

  }

  dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */



  /* Compute lookahead tables to speed up decoding.

   * First we set all the table entries to 0, indicating "too long";

   * then we iterate through the Huffman codes that are short enough and

   * fill in all the entries that correspond to bit sequences starting

   * with that code.

   */



  MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));



  p = 0;

  for (l = 1; l <= HUFF_LOOKAHEAD; l++) {

    for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {

      /* l = current code's length, p = its index in huffcode[] & huffval[]. */

      /* Generate left-justified code followed by all possible bit sequences */

      lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);

      for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {

	dtbl->look_nbits[lookbits] = l;

	dtbl->look_sym[lookbits] = htbl->huffval[p];

	lookbits++;

      }

    }

  }

}





/*

 * Out-of-line code for bit fetching (shared with jdphuff.c).

 * See jdhuff.h for info about usage.

 * Note: current values of get_buffer and bits_left are passed as parameters,

 * but are returned in the corresponding fields of the state struct.

 *

 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width

 * of get_buffer to be used.  (On machines with wider words, an even larger

 * buffer could be used.)  However, on some machines 32-bit shifts are

 * quite slow and take time proportional to the number of places shifted.

 * (This is true with most PC compilers, for instance.)  In this case it may

 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the

 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.

 */



#ifdef SLOW_SHIFT_32

#define MIN_GET_BITS  15	/* minimum allowable value */

#else

#define MIN_GET_BITS  (BIT_BUF_SIZE-7)

#endif





GLOBAL boolean

jpeg_fill_bit_buffer (bitread_working_state * state,

		      register bit_buf_type get_buffer, register int bits_left,

		      int nbits)

/* Load up the bit buffer to a depth of at least nbits */

{

  /* Copy heavily used state fields into locals (hopefully registers) */

  register const JOCTET * next_input_byte = state->next_input_byte;

  register size_t bytes_in_buffer = state->bytes_in_buffer;

  register int c;



  /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */

  /* (It is assumed that no request will be for more than that many bits.) */



  while (bits_left < MIN_GET_BITS) {

    /* Attempt to read a byte */

    if (state->unread_marker != 0)

      goto no_more_data;	/* can't advance past a marker */



    if (bytes_in_buffer == 0) {

      if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))

	return FALSE;

      next_input_byte = state->cinfo->src->next_input_byte;

      bytes_in_buffer = state->cinfo->src->bytes_in_buffer;

    }

    bytes_in_buffer--;

    c = GETJOCTET(*next_input_byte++);



    /* If it's 0xFF, check and discard stuffed zero byte */

    if (c == 0xFF) {

      do {

	if (bytes_in_buffer == 0) {

	  if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))

	    return FALSE;

	  next_input_byte = state->cinfo->src->next_input_byte;

	  bytes_in_buffer = state->cinfo->src->bytes_in_buffer;

	}

	bytes_in_buffer--;

	c = GETJOCTET(*next_input_byte++);

      } while (c == 0xFF);



      if (c == 0) {

	/* Found FF/00, which represents an FF data byte */

	c = 0xFF;

      } else {

	/* Oops, it's actually a marker indicating end of compressed data. */

	/* Better put it back for use later */

	state->unread_marker = c;



      no_more_data:

	/* There should be enough bits still left in the data segment; */

	/* if so, just break out of the outer while loop. */

	if (bits_left >= nbits)

	  break;

	/* Uh-oh.  Report corrupted data to user and stuff zeroes into

	 * the data stream, so that we can produce some kind of image.

	 * Note that this code will be repeated for each byte demanded

	 * for the rest of the segment.  We use a nonvolatile flag to ensure

	 * that only one warning message appears.

	 */

	if (! *(state->printed_eod_ptr)) {

	  WARNMS(state->cinfo, JWRN_HIT_MARKER);

	  *(state->printed_eod_ptr) = TRUE;

	}

	c = 0;			/* insert a zero byte into bit buffer */

      }

    }



    /* OK, load c into get_buffer */

    get_buffer = (get_buffer << 8) | c;

    bits_left += 8;

  }



  /* Unload the local registers */

  state->next_input_byte = next_input_byte;

  state->bytes_in_buffer = bytes_in_buffer;

  state->get_buffer = get_buffer;

  state->bits_left = bits_left;



  return TRUE;

}





/*

 * Out-of-line code for Huffman code decoding.

 * See jdhuff.h for info about usage.

 */



GLOBAL int

jpeg_huff_decode (bitread_working_state * state,

		  register bit_buf_type get_buffer, register int bits_left,

		  d_derived_tbl * htbl, int min_bits)

{

  register int l = min_bits;

  register INT32 code;



  /* HUFF_DECODE has determined that the code is at least min_bits */

  /* bits long, so fetch that many bits in one swoop. */



  CHECK_BIT_BUFFER(*state, l, return -1);

  code = GET_BITS(l);



  /* Collect the rest of the Huffman code one bit at a time. */

  /* This is per Figure F.16 in the JPEG spec. */



  while (code > htbl->maxcode[l]) {

    code <<= 1;

    CHECK_BIT_BUFFER(*state, 1, return -1);

    code |= GET_BITS(1);

    l++;

  }



  /* Unload the local registers */

  state->get_buffer = get_buffer;

  state->bits_left = bits_left;



  /* With garbage input we may reach the sentinel value l = 17. */



  if (l > 16) {

    WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);

    return 0;			/* fake a zero as the safest result */

  }



  return htbl->pub->huffval[ htbl->valptr[l] +

			    ((int) (code - htbl->mincode[l])) ];

}





/*

 * Figure F.12: extend sign bit.

 * On some machines, a shift and add will be faster than a table lookup.

 */



#ifdef AVOID_TABLES



#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))



#else



#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))



static const int extend_test[16] =   /* entry n is 2**(n-1) */

  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,

    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };



static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */

  { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,

    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,

    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,

    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };



#endif /* AVOID_TABLES */





/*

 * Check for a restart marker & resynchronize decoder.

 * Returns FALSE if must suspend.

 */



LOCAL boolean

process_restart (j_decompress_ptr cinfo)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  int ci;



  /* Throw away any unused bits remaining in bit buffer; */

  /* include any full bytes in next_marker's count of discarded bytes */

  cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;

  entropy->bitstate.bits_left = 0;



  /* Advance past the RSTn marker */

  if (! (*cinfo->marker->read_restart_marker) (cinfo))

    return FALSE;



  /* Re-initialize DC predictions to 0 */

  for (ci = 0; ci < cinfo->comps_in_scan; ci++)

    entropy->saved.last_dc_val[ci] = 0;



  /* Reset restart counter */

  entropy->restarts_to_go = cinfo->restart_interval;



  /* Next segment can get another out-of-data warning */

  entropy->bitstate.printed_eod = FALSE;



  return TRUE;

}





/*

 * Decode and return one MCU's worth of Huffman-compressed coefficients.

 * The coefficients are reordered from zigzag order into natural array order,

 * but are not dequantized.

 *

 * The i'th block of the MCU is stored into the block pointed to by

 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.

 * (Wholesale zeroing is usually a little faster than retail...)

 *

 * Returns FALSE if data source requested suspension.  In that case no

 * changes have been made to permanent state.  (Exception: some output

 * coefficients may already have been assigned.  This is harmless for

 * this module, since we'll just re-assign them on the next call.)

 */



METHODDEF boolean

decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)

{

  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

  register int s, k, r;

  int blkn, ci;

  JBLOCKROW block;

  BITREAD_STATE_VARS;

  savable_state state;

  d_derived_tbl * dctbl;

  d_derived_tbl * actbl;

  jpeg_component_info * compptr;



  /* Process restart marker if needed; may have to suspend */

  if (cinfo->restart_interval) {

    if (entropy->restarts_to_go == 0)

      if (! process_restart(cinfo))

	return FALSE;

  }



  /* Load up working state */

  BITREAD_LOAD_STATE(cinfo,entropy->bitstate);

  ASSIGN_STATE(state, entropy->saved);



  /* Outer loop handles each block in the MCU */



  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

    block = MCU_data[blkn];

    ci = cinfo->MCU_membership[blkn];

    compptr = cinfo->cur_comp_info[ci];

    dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];

    actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];



    /* Decode a single block's worth of coefficients */



    /* Section F.2.2.1: decode the DC coefficient difference */

    HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);

    if (s) {

      CHECK_BIT_BUFFER(br_state, s, return FALSE);

      r = GET_BITS(s);

      s = HUFF_EXTEND(r, s);

    }



    /* Shortcut if component's values are not interesting */

    if (! compptr->component_needed)

      goto skip_ACs;



    /* Convert DC difference to actual value, update last_dc_val */

    s += state.last_dc_val[ci];

    state.last_dc_val[ci] = s;

    /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */

    (*block)[0] = (JCOEF) s;



    /* Do we need to decode the AC coefficients for this component? */

    if (compptr->DCT_scaled_size > 1) {



      /* Section F.2.2.2: decode the AC coefficients */

      /* Since zeroes are skipped, output area must be cleared beforehand */

      for (k = 1; k < DCTSIZE2; k++) {

	HUFF_DECODE(s, br_state, actbl, return FALSE, label2);

      

	r = s >> 4;

	s &= 15;

      

	if (s) {

	  k += r;

	  CHECK_BIT_BUFFER(br_state, s, return FALSE);

	  r = GET_BITS(s);

	  s = HUFF_EXTEND(r, s);

	  /* Output coefficient in natural (dezigzagged) order.

	   * Note: the extra entries in jpeg_natural_order[] will save us

	   * if k >= DCTSIZE2, which could happen if the data is corrupted.

	   */

	  (*block)[jpeg_natural_order[k]] = (JCOEF) s;

	} else {

	  if (r != 15)

	    break;

	  k += 15;

	}

      }



    } else {

skip_ACs:



      /* Section F.2.2.2: decode the AC coefficients */

      /* In this path we just discard the values */

      for (k = 1; k < DCTSIZE2; k++) {

	HUFF_DECODE(s, br_state, actbl, return FALSE, label3);

      

	r = s >> 4;

	s &= 15;

      

	if (s) {

	  k += r;

	  CHECK_BIT_BUFFER(br_state, s, return FALSE);

	  DROP_BITS(s);

	} else {

	  if (r != 15)

	    break;

	  k += 15;

	}

      }



    }

  }



  /* Completed MCU, so update state */

  BITREAD_SAVE_STATE(cinfo,entropy->bitstate);

  ASSIGN_STATE(entropy->saved, state);



  /* Account for restart interval (no-op if not using restarts) */

  entropy->restarts_to_go--;



  return TRUE;

}





/*

 * Module initialization routine for Huffman entropy decoding.

 */



GLOBAL void

jinit_huff_decoder (j_decompress_ptr cinfo)

{

  huff_entropy_ptr entropy;

  int i;



  entropy = (huff_entropy_ptr)

    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				SIZEOF(huff_entropy_decoder));

  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;

  entropy->pub.start_pass = start_pass_huff_decoder;

  entropy->pub.decode_mcu = decode_mcu;



  /* Mark tables unallocated */

  for (i = 0; i < NUM_HUFF_TBLS; i++) {

    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;

  }

}

